Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $34.85   4.711%   $36.4918   $36.49   $36.50   $36.50  
  Purchase #2 $63.26   5.660%   $66.8405   $66.84   $66.85   $66.80  
  Purchase #3 $49.54   7.184%   $53.099   $53.10   $53.10   $53.10  
  Purchase #4 $206.92   13.111%   $234.0493   $234.05   $234.05   $234.00  
  Purchase #5 $93.70   12.704%   $105.6036   $105.60   $105.60   $105.60  
  Purchase #6 $202.42   9.608%   $221.8685   $221.87   $221.85   $221.90  
  Purchase #7 $149.94   4.594%   $156.8282   $156.83   $156.85   $156.80  
  7 purchase totals = $800.63       $874.7809   $874.78   $874.80   $874.70